1. Field of the Invention
The present invention relates to a novel optically active polymaleimide derivative and a method for its production. The optically active polymaleimide derivative is expected to be useful for e.g. a separating medium.
2. Discussion of Background
It is known that an optically active polymaleimide polymer having a certain degree of specific rotation, can be produced by radical polymerization or anionic polymerization using optically active (R)-(+)-N-xcex1-methylbenzylmaleimide as the starting material (T. Oishi et al., J. Polym. Chem. Ed., 22, 2789-2800 (1984)).
On the other hand, a method for obtaining an optically active polymaleimide derivative by asymmetric anionic polymerization of an achiral maleimide derivative, is also known (T. Oishi et al., Chemistry Letters, 1998, 791-792).
However, by the radical polymerization method using optically active (R)-(+)-N-xcex1-methylbenzylmaleimide as the starting material and employing azoisobutyronitrile, the product obtained is of such a low level that the specific rotation ([xcex1]43525) is not more than +30xc2x0, and the number average molecular weight (Mn) as calculated as standard polystyrene is up to about 3,000.
Further, also by the anionic polymerization using the same starting material and employing butyl lithium, the product obtained is of such a level that the specific rotation is from 0 to xe2x88x92100xc2x0, and the molecular weight (Mn) is not more than 3xc3x97103. Thus, optically active polymaleimide derivatives obtained by these conventional methods were not satisfactory with respect to both optical purities and molecular weights, when application to e.g. a separating medium, was taken into account.
On the other hand, by the method for obtaining an optically active polymaleimide derivative by asymmetric anionic polymerization using an achiral maleimide derivative, it is possible to obtain an optically active polymer having a certain degree of specific rotation, but the molecular weight is as low as about 1xc3x97103. Further, no case is known wherein the same method is applied by using an optically active maleimide derivative as a starting material.
The present inventors have conducted an extensive study to develop an optically active poly(N-xcex1-methylbenzylmaleimide) having a higher optical purity and molecular weight, and as a result, have found it possible to obtain an optically active poly(N-xcex1-methylbenzylmaleimide) having a high specific rotation and a high molecular weight by using optically active (S)-(xe2x88x92)-N-xcex1-methylbenzylmaleimide as the starting material and carrying out anionic polymerization in the presence of an asymmetric ligand. The present invention has been accomplished on the basis of this discovery.
Namely, the present invention provides an optically active poly(N-xcex1-methylbenzylmaleimide) represented by the following formula (1): 
wherein n is a number within a range of from 2 to 10,000, and symbol * represents optically active carbon, and having a specific rotation ([xcex1]43525) of at least +30xc2x0.
Further, the present invention provides a method for producing the above-mentioned optically active poly(N-xcex1-methylbenzylmaleimide), which comprises subjecting (S)-(xe2x88x92)-N-xcex1-methylbenzylmaleimide of the following formula (2): 
to anionic polymerization in the presence of an asymmetric ligand.